Expansion cards are inserted into a card bay in an electronic system, such as a computer system, to enable one or more microprocessors to be connected to external devices. Generally, expansion cards permit expanded performance from a computer system through connection with external devices. A peripheral component interconnect (PCI) system is one example of a system configured to expand the utility of a computer system through connection with external devices. A PCI system includes PCI slots that are externally accessible for reception of PCI cards. PCI cards are inserted into a card bay of the PCI system. Compatible external devices can be plugged into the PCI cards, which are one type of expansion card. Expansion cards that do not span the full length of the card bay that they are inserted into are known as short cards.
A computer system typically comprises a chassis for structural support, a central processing unit (CPU), various cooling fans, a card bay to house removable printed circuit assemblies (PCA), and an array of other electrical components. The card bay is designed to receive removable printed circuit cards, such as input/output (I/O) cards. The card bay provides card guides on one side that are aligned to coordinate with the bulkhead guides on the opposing, or bullhead, side. In practice, an expansion card would typically be inserted into the computer system card bay by coupling one edge of the expansion card to the bulkhead guide and coupling the opposing edge of the expansion card to the complementary card guide on the other side of the card bay. The expansion card is then mechanically and electrically coupled to the computer at the backplane, or mid-plane, or generally, at the connector plane. Therefore, a card that spans the full length of the card bay is typically supported on three edges.
Expansion cards are uniquely configured to support specific applications, and hence, not all expansion cards are the same size. Indeed, some expansion cards do not span the full length of the card bay of the computer system. Such expansion cards, known as short cards, are supported only on two edges; the one edge mechanically coupled by the bulkhead guide and the second edge mechanically and electrically coupled to the connector plane. Therefore, short cards installed in a computer system have at least one unsupported edge and are susceptible to bending and damage when subjected to harsh forces.
A computer system suitable for service in a harsh environment, especially a computer system employed in telecommunications, is typically qualified for operation in the harsh environment. Harsh environments can be encountered in deploying mobile computers, such as computers mounted on delivery trucks, machine shop applications where the computers are subjected to vibrations, computer systems located in earthquake zones, and any situation that would subject the computer system to bumps, drops or large amplitude vibrations. The military and government agencies deploy a wide variety of computers and telecommunication equipment in diverse environments, and the military and government agencies encourage suppliers to employ both widely available components and cards, as well as the best value components and cards. Consequently, short cards are often installed in computer and telecommunication systems that are subjected to harsh environments. In addition, implementation of these computer and telecommunication systems is subject to qualification with certain performance specifications.
Performance specifications for a variety of measurable system parameters can be specified by the military or government agencies, or by industry groups. For example, all electronic equipment has the potential to interfere with other electronic equipment. Interference can be caused by electromagnetic radiation, the grounding system, the electrical power connection, excessive heat or insufficient airflow, and connecting wires or cables. The Federal Communications Commission (FCC) regulates a portion of this through Part 15 of their rules and regulations. FCC Part 15 specifies a maximum allowable amount of electromagnetic radiation from an electronic device in a commercial or residential environment at specific frequencies.
Network Equipment Building System (NEBS) is an industry standard that addresses the issue of collocated electronic equipment. Telephone companies typically place a large amount of network equipment, often from different manufacturers, into relatively tight association especially in their central office buildings. To account for this, they gathered input from the FCC and various national and international trade and standards groups to create a set of specifications for network facilities-located equipment. Originally developed by Bell Telephone laboratories in the 1970s and expanded by Bellcore, this standard is known as NEBS, or NEBS criteria.
The rigorous NEBS criteria have become a universal measure of network product excellence. NEBS compliance is required for equipment deployed in the central office in the North American Public Switched Network. NEBS compliance is an advantage for access providers including Local Exchange Carriers (LECs), Competitive Access Providers (CAPs), Competitive Local Exchange Carriers (CLECs), Internet Service Providers (ISPs), and Access Service Providers (ASPs). Products that are NEBS compliant are also expected to be top performers in network environments. The NEBS criteria are the most referenced documents in the United States Telecomnmunications Industry on the subject, and are designed to help ensure that telecom equipment is easy to install, operates reliably, and efficiently occupies building space. The expectation is that specifications for equipment configuration and compatibility will simplify product installation and reduce maintenance costs.
Regional operating companies and inter-exchange carriers insist upon NEBS compliance. NEBS is a baseline for vendor selection and deployment by service providers such as CLECs, ISPs, and independent telephone companies and others.
Even more stringent than the FCC Part 15 requirements, NEBS addresses a wide range of parameters related to personal safety, protection of property, and operational continuity. The NEBS criteria specifies parameters for space planning, temperature, humidity, fire, earthquake, vibration, transportation acoustics, air quality, and illumination as well as electrostatic discharge (ESD), electromagnetic interference (EMI), lightning and AC power fault, steady state power induction, corrosion direct current potential difference, and electrical safety in configuring telecommunication devices.
With the above in mind, one approach that the computer system industry has taken is to select and insert a best value short card and leave it unsupported on one edge. This method allows a wide variety of cards to be installed in the computer systems and enables the manufacturers to select the best value components. However, when the short cards are unsupported on one edge, the computer system is unlikely to meet the NEBS criteria for use in harsh environments, and so, the lack of robustness limits the utility of the computer system in the marketplace.
Another approach taken by the computer system industry is to select only full-length cards that will be supported on three edges by the bulkhead guides, card guides, and the connector plane. This approach ensures that the full-length cards are adequately supported, but limits the selection and value of the cards that may be installed in the computer system. Therefore, the computer system may meet the NEBS criteria, but may not offer the consumer the breadth of applications they require and may not offer sufficient value.
For the reasons stated above and for other reasons presented in this disclosure, a need exists for computer systems qualified for use in harsh environments that employ varying length printed circuit cards including short cards.